Moving-coil electrical instruments



Filed June 10, 1957 INVENTOR Lawrence J. Luncls WITNESSES BY W 9 4;

ATTORN EY United Sttes Patent MOVING-COIL ELECTRICAL INSTRUMENTSLawrence J. Lunas, Cedar Grove, N.J., assignor to Westinghouse ElectricCorporation, East Pittsburgh, Pa., a corporation of Pennsylvania FiledJune 10, 1957, Ser. No. 664,759

1 Claim. (Cl. 324-150) This invention relates to moving-coil electricalinstruments and has particular relation to moving-coil electricalmeasuring instruments wherein a coil side is disposed for rotation in anair gap of a magnetic structure.

In many instruments it has been found desirable to provide an air gapdefined by a magnetic pole piece and a source of magnetomotive forcewhich surrounds the pole piece to establish a magnetic field in the airgap. A moving coil has a coil side disposed in the air gap and ismounted for rotation relative to the magnetic pole piece. Suchinstruments have been found useful as relays and in other fields and theinvention is applicable thereto. However, the invention is particularlysuitable for an electrical measuring instrument of the foregoing typeand will be discussed with reference to such a measuring instrument.

'In instruments heretofore constructed, a radially magnetized permanentmagnet has been positioned intermediate a pair of inner and outermagnetic pole pieces. The inner pole piece is spaced from the innerperiphery of the magnet to define an air gap for an outer coil side of amoving coil. The coil has an opposed inner coil side which is positionedin an opening of the inner pole piece. .In such instruments, the problemarises as to the manner of installing and removing the moving coil withrespect to the inner pole piece.

'In instruments of this type previously constructed, the inner polepiece is provided with a slot extending from the outer periphery to thecentral opening of the inner pole piece. This slot is proportioned topermit passage of the inner coil side of the moving coil into theopening of the inner pole piece for permitting assembly of the coil withrespect to the inner pole piece. A mag netic plug ordinarily formed of ahigh permeability material is inserted into the slot subsequent toinstallation of the moving coil to close the slot for providing anefficient magnetic circuit. It has been observed, however, that withprevious arrangements of the type described, the slot has not beensufficiently closed by the magnetic plug to obtain a magnetic circuit ofthe desired efficiency.

In accordance with the present invention, a moving co'il instrument isprovided with improved means for permitting the installation and removalof the moving coil. In a preferred embodiment of the invention, an innermagnetic pole piece is surrounded by a substantially C-shaped permanentmagnet with the inner membar and magnet in spaced relation to define anair gap. The magnet is surrounded by and is in engagement with an outermagnetic member which is integrally connected to the inner magneticmember. The inner member includes a slot which extends from the outerperiphery thereof to a central opening of the inner member to permit theinstallation and removal of a moving coil with respect to the innermember.

In order to provide an efficient magnetic circuit, the inventionprovides that the side walls of the slot have ice 'fit condition tothereby effectively close the slot for providing an efficient magneticcircuit. The plug is preferably formed of a high permeability magneticmaterial such as soft iron.

It is therefore an object of the invention to provide a moving-coilelectrical instrument of improved construction.

It is another object of the invention to provide a moving-coilinstrument having a magnetic circuit with improved means permitting theinstallation and removal of the coil with respect to the magneticcircuit.

It is a further object of the invention to provide a moving-coilinstrument having a magnetic circuit including a magnetic member havinga slot through which the moving coil may be assembled to the member withimproved means permitting effective closure of the slot subsequent toassembly of the coil.

Other objects of the invention will become apparent from the followingdescription taken in conjunction with the accompanying drawings, inwhich:

Figure 1 is a view in top plan of an electrical instrument embodying theteachings of the invention;

Fig. 2 is a view taken along the line II-II of Fig. l; and

Fig. 3 is an exploded view in perspective of a magnetic member andassociated magnetic plug of the instrument of Figs. 1 and 2.

Referring to the drawings, there is illustrated in Fig. 1 an electricalmeasuring instrument of the moving-coil type represented generally bythe numeral 1 embodying the teachings of the present invention. theinstrument 1 includes a source of magnetomotive force comprising apermanent magnet 3 constructed of any suitable permanent magnetmaterial. The magnet 3 is preferably of substantially C-shapedconfiguration having an opening 5 bounded by the inner periphery 7 ofthe magnet. The magnet 3 further includes an outer periphery 9 and anopen side 11. netized such that magnetic flux traversed the magnet indirections extending radially of the axis of the magnet.

In order to provide a magnetic path for magnetic flux emanating from themagnet 3, a suitable magnetic structure is provided. This structureincludes an inner magnetic member or pole piece 13 constructed of asuitable magnetic material such as soft iron. The member 13 is ofsubstantially ring-shaped configuration having a central opening 15 andan outer periphery 17. As shown in Fig. 1, the member 13 is positionedwithin the opening 5 of the magnet 3 to be surrounded by the magnet 3.The outer periphery 17 of the member 13 is spaced A from the innerperiphery 7 of the magnet 3 to define an air gap 19 which is arcuateabout the axis of the magnet 3.

The magnetic structure includes further an outer ringshaped member orpole piece 21 which may also be formed of soft iron. The member 21 has acentral opening 23 bounded by the inner periphery 25 of the member 21.The magnet 3 is positioned within the opening 23 of the member 21 withthe outer periphery 9 of the magnet in engagement with the innerperiphery 25 of the member 21.

The members 13 and 21 are preferably magnetically connected to provide alow reluctance path for flux of the magnet 3. For this purpose, themembers 13 and 21 are conveniently integrally connected to provide amagnetic circuit of one-piece construction. As shown in Fig. 1, aconnecting neck portion 29 extends from the inner periphery 25 of themember 21 to the outer periph-.

As there shown,

The magnet 3 is mag-.

cry 17 of the member 13 to connect the members 13 and 21,

The one-piece magnetic circuit comprising the parts 13, 21 and 29 ispreferably formed of a plurality of identical magnetic laminations 30.Each of these laminations has the configuration shown in Fig. 1.

The instrument 1 further includes a moving-coil 31 of substantiallyrectangular configuration as shown in Fig. 2. The coil 31 includes aninner coil side 33 and an outer coil side 35 which define a pair ofspaced parallel axes. It is noted that the inner coil side 33 ispositioned to extend through the opening of the member 13 with the outercoil side 35 positioned in the air gap 19.

'In order to mount the coil 31 for rotation to carry the coil side 35through the air gap 19, the coil 31 is secured to a shaft 37. As bestshown in Fig, 2, the shaft 37 extends through the opening 15 of themember 13 concentrically of the axis of the opening 15 and is supportedat its ends by a pair of spaced bearing members 39 and 41. With thisarrangement, when the coil 31 is energized the coil side 35 will movethrough the air gap 19 about the axis of the shaft 37 relative to themagnet 3 and relative to the inner and outer members 13 and 21.

In order to permit an indication of the magnitude of an electricalquantity energizing th coil 31, a suitable pointer 43 is secured to theshaft 37 for movement with the coil 31. The pointer 43 moves withrespect to a suitably calibrated scale 45 to indicate the magnitude ofthe energizing quantity. With the arrangement as described, aninstrument is provided having a substantially circular scale with arange of movement of the pointer 43 of approximately 270 C. A suitablecontrol spring 48 is provided to oppose movement of the pointer 43 as isunderstood in the art.

In order to permit installation and removal of the coil 31 with respectto the inner member 13, a suitable slot 47 is provided in the member 13which extends from the outer periphery 17 to the opening 15. The slotmay be located at any angular position about the axis of the shaft 37.Preferably, however, the slot is formed in the member 13 at the openside 11 of the magnet 3 adjacent the connecting neck 29. The slot isproportioned to permit passage of the inner coil side 33 of the coilthrough the slot relative to the opening 15 of the member 13.

In accordance with the invention, the slot 47 includes a pair of sidewalls 49 and 51 which are cut away or recessed to provide recesses 53and 55 of the side walls of arcuate configuration. This construction isbest shown in Fig. 3. The recesses 53 and 55 are preferably configuredso as to define a passage 57 of cylindrical configuration having an axisextending transverse to the direction of extension of the slot 47.

The passage 57 and slot 47 may conveniently b formed by a singlestamping operation wherein material of each lamination is removed toprovide the properly configured slot and passage.

In order to close the magnetic circuit provided by the member 13subsequent to installation of the coil 31 through the slot 47, theinvention provides a magnetic plug 59 proportioned to substantiallyentirely fill the passage 57. The plug 59 is preferably formed of a highpermeability magnetic material such as soft iron,

The present invention provides that the plug 59 is in the form of acylinder having a radius substantially equal to the radius of thecylindrical passage 57. This arrangement provides a press fit conditionof the plug 59 to thereby permit the installation and removal of theplug 59 relative to the passage 57. Such arrangement further provides avery efiicient magnetic circuit inasmuch as the plug 59 substantiallyentirely fills the passage 57 with extremely small clearance between theplug and the walls of the recesses 53 and 55. The axial dimension of theplug 59 is selected to be substantially equal to the thickness dimensionof the pole piece 13. By providing cylindrical configurations of thepassag 57 and plug 59 extremely accurate dimensions may be obtained forthe plug and passage.

Although the invention has been described with reference to certainspecific embodiments thereof, numerous modifications are possible and itis desired to cover all modifications falling within the spirit andscope of the invention.

I claim as my invention:

In an electrical instrument, a source of magnetomotive force, aparamagnetic body providing a magnetic path for magnetic flux producedby said source, said body comprising an outerbody portion having anaperture therein and having a substantially ring-shaped portion locatedin said aperture, said ring-shaped portion having a first openingdefining an inner periphery, said ringshaped portion having an outerperiphery providing a side wall of an air gap arcuate about an axisextending parallel to said first opening and located in said aperture, acoil having an inner coil side positioned in said first opening and anouter coil side positioned in said air gap, means mounting said coil forrotation about said axis to carry said outer coil side through said airgap relative to said source and ring-shaped portion, said ring-shapedportion having a passageway completely cutting thereacross through whicha portion of said coil may be passed to permit said coil and saidring-shaped portion to be assembled, the portions of said ring-shapedportion adjacent said passageway forming spaced walls, each said wallcomprising spaced surface portions and a circularly cylindricalintermediate surface portion connecting said spaced surface portions,said cylindrical surface portions having a common axis of curvature andcomprising a substantial portion of said walls, and a fully circularlycylindrical paramagnetic closure member of a diameter to lie whollywithin said passageway and to substantially fill the cross section ofsaid passageway, the wall portions of said closure member adjacent saidcylindrical surface portions seating snugly thereagainst.

References Cited in the file of this patent

